Manufacturers are now increasing the requirements for case materials for information technology equipment, such as for example printers, copiers, Notebooks, monitors, mobile phones etc. Many of these require flame-retarding properties. The demand for materials containing halogen-free flame-retardants is met particularly by PC+ABS blends, which have flame-resistance provided by organic phosphoric acid esters. Such compositions have been disclosed is many publications including EP-A 0 345 522, EP-A 0 640 655 and EP 0 363 608. Molded bodies produced from such compositions have a good combination of application properties, such as good toughness, high resistance to thermal stresses and satisfactory processing behavior for many applications, but generally only within a limited processing window.
More recently, the requirements for resistance to chemicals and hydrolysis, and for injection molding behavior and processing stability i.e. the consistency of the characteristics of such molding compositions at high processing temperatures, have increased. These requirements are met by PC/ABS compositions containing organic phosphoric acid esters, in particular oligomeric phosphates, as a flame retardant, which contain an ABS produced by the mass polymerization process as the ABS component. Such compositions have also already been disclosed in patent literature.
Thus EP-A 0 755 977 discloses PC+ABS blends containing ABS of a low rubber content, preferably mass ABS, and a low flame-retardant content. The required melt flowability is achieved in these molding compositions by using polycarbonate with a relatively low molecular weight, most preferably having weight average molecular weights of <25,000 g/mol, which restricts the stress cracking resistance. A combination of stress cracking resistance and flame-resistance that is sufficient for many, but not all, applications is obtained only by restricting the content of flame-retardant and rubber. The current increased requirements for melt flowability, flame-resistance and stress cracking resistance are no longer met by such compositions. Although the stress cracking resistance is improved by the use of higher-molecular polycarbonate, the melt flowability is reduced still further. Using higher quantities of flame retardant meets the flowability requirements but results in a reduction in resistance to chemicals.
EP-A 0 933 396 discloses polycarbonate mixtures containing mass ABS and oligophosphate flame retardants characterized by good notched impact resistance, resistance to hydrolysis and improved processing stability. However, the molding compositions disclosed in this application have in particular inadequate flame-resistance and weld line strength for many applications.
JP-A 11 302 523 discloses compositions of polycarbonate, mass ABS, emulsion ABS and an acrylonitrile-vinyl copolymer, which contain monophosphate and polytetrafluoroethylene (PTFE) flame-retardants. These molding compositions have an inadequate processing window, as they have a tendency to phase agglomeration at higher processing temperatures, which impairs the mechanical properties, and bleeds out the flame-retarding additive. Furthermore, experience shows that such compositions have inadequate resistance to hydrolysis.
DE 198 53 105 A1 discloses compositions containing polycarbonate, mass ABS, which is preferably used in combination with emulsion ABS, and phosphoric acid esters. These molding compositions have, in particular, inadequate flowability, resistance to chemicals and to hydrolysis and poor creep behavior.
EP-A 1 026 205 discloses molding compositions of polycarbonate, ABS graft polymers, preferably produced by the mass polymerization process, monomeric or oligomeric phosphoric acid esters and silicate reinforcing materials, which are characterized in that the chlorine content of the composition is no greater than 100 ppm. Compositions containing acrylate-based graft polymers with a core/shell structure as a further component are also disclosed. The molding compositions thus disclosed are characterized by excellent resistance to hydrolysis, but generally exhibit poor resistance to chemicals and inadequate creep behavior as a result of the low molecular weight of the polycarbonate used. However, the low molecular weight is necessary to achieve sufficient melt flowability. With the mass ABS used in these compositions it is impossible to achieve an adequate flowability level using higher-molecular polycarbonate. The same applies also to the molding compositions disclosed in WO 00/39210, which are characterized in that they contain a bisphenol A-bridged oligophosphate with a low acid value as the flame-retarding additive.
U.S. Pat. No. 5,849,827 discloses flame-resistant compositions containing polycarbonate and emulsion ABS, which, in addition to conventional flame-retarding additives, contain very fine inorganic particles and are characterized by improved flame resistance. Positive effects of the particles on the melt flowability and resistance to hydrolysis of the molding compositions are not disclosed in this application.
The object of the present invention was to provide polycarbonate compositions, which are characterized in particular by a combination of excellent stress cracking resistance and creep resistance with improved melt flowability and which also have a high degree of toughness, processing stability and resistance to hydrolysis. In particular, the object of the invention was to provide flame-resistant compositions from which molded articles may be produced, which pass the UL94V test at 1.5 mm wall thickness with a V−0 rating and in which the flame-retarding additive does not bleed out significantly under the conventional processing conditions.